Micrometer



April 30, 1946. D.. A. LUTTON MICROMETER Filed Feb. l2, 1944 2 Sheets-Sheet `1 Dnald A Luttnn April 30, 1946. D. A. LUT'roN MIcRoMETER Filed Feb. 12, 1944 2 Sheets-Sheet El Unnald A Luttcm Patentedl Apr. 30, 1946 UNITED STATES PATENT OFFICE MICROMETER Donald A. Lutton, Winthrop, Mass.

Application February 12, 1944, Serial No. 522,083

(Granted under the act of March 3, 1883, as amended April 30, 1928; 370 0. G. 757) 1 Claim.

The invention described herein may be manufactured and used by or for the Government for governmental purposes without the payment to me of any royalty thereon.

This invention relates to an improved micrometer by means of which the feel that is exercised by a skilled mechanic in attaining the ultimate precision of measurement of which the instrument is capable, is made available to any novice operator by a mechanical device. Hence the inexperienced and unskilled operator may readily measure with the improved micrometer with the same precision as that obtained by the skilled mechanic.

When using a Vernier micrometer, the ability to feel the pressure exerted by the spindle thru the work against the anvil is the determining factor in the ability of the operator to correctly measure to the ten-thousandth part of an inch. The spindle isset against the work so that the pressure is transmitted thru the work to the anvil, the setting being accomplished by turning the sleeve which'is integral with the spindle and screw. The torque exerted on the sleeve by the fingers of the operator is transmitted thru the screw to the spindle, hence the compressive force exerted by the spindle is proportional to the torque applied to the sleeve. Therefore, the sensitiveness of the operators ngers determines the ability of the operator to accurately adjust the torque so that the stress applied to, and the corresponding strain or yield developed in the instrument and in the piece being measured, will be uniform instead of varying between successive measurements.

Accordingly, it is an object of this invention to provide an improved micrometer which will enable the inexperienced operator to consistently obtain the same precision in measurements as are expected of a skilled operator.

, A particular object of this invention is to pro-- vide an improved micrometer having a dial indication 'of the amount of pressure exerted on the piece` to be measured.

The specific nature of the invention as well as other objects and advantages thereof will clearly appear fro-m a description of a preferred embodiment as shown in the accompanying drawings in which:

Fig. 1 is a side elevational view of the complete micrometer with a portion of the barrel broken away.

Fig. 2 is a top elevational view of the micronieter.

operate with the threads of the nut 2.

Fig. 3 is a sectional view taken along the plane 3-3 of Fig 2.

Figs. 4 thru 7 are sectional views taken along the planes 4-4, 5 5', 6 6, and 'I-'I of Fig. 3 respectively.

Fig. 8 is an enlarged top elevational view of the dial indicator.

Figs. 9 and 10 are sectional views taken along the planes 9-9 and III-I0 respectively of Fig. 8.

In Fig. 1 is shown in assembled relation a micrometer embodying this invention. The micrometer consists of theusual frame I', nut 2, spindle 3, and sleeve 4, and in addition the spring 5, collet 6, push-rod 'I,and pin 3, and the` dial indicator 22.

More specifically, the frame I is of the usual U-form with an anvil 45 formed o'n one arm and a hollow cylinder 9 formed on the other arm. The cylinder 9 carries the Yusual scale graduations 49 but in construction varies considerably from the usual micrometer. -The interior of cylinder 9 is Shaped to produce three internal adjacent sectors I 0, II, andr I2 of diierent diameters. Threads I3 are provided in the end of section I2. A nut 2 is inserted into section I2 and is finished to a size that will allow it to turn and slide freely in this space. In the side of the nut 2 is inserted a pin 8 which, in assembly, ts into a longitudinal slot I6 in the wall of cylinder 9 thereby permitting limited longitudinal movement of the nut 2 within section I2. Nut.l2 is provided with interior micrometer threads I5. A collet 6 is screwed into the threads :I3 in the end of cylinder 9. A spring 5 is mounted between nut 2 and collet 6. In the back end of the nut 2 is a pin hole I1 into which'ts one nub I8 of the spring 5.V The other nub I9 ts into a pin hole 20 in the collet 6. The spring 5 is assembled under a combined' compressive and torsional stress for a purpose tobe described.

A spindle 3 is mountedV within the cylinder 9, being' supported in bearing relation by the vsection I U. Spindle 3 extends into section I2 of cylinder 9`and on this portion of the spindle, micrometer threads 47 are provided which co.

Ihelextreme end of spindle 3 is secured in conventional fashion to the base of hollow sleeve or barrel l or can `be integral therewith. Sleeve 4 surrounds cylinder 9 and Vernier graduations 48 are provided on the forward rim of sleeve 4 to co'- operate with graduations 49.

The end of the arm of the frame I on which the cylinder 9 is provided, is enlarged to form a cylindrical recess 2| A dial indicator 22 is inserted in recess 2| and secured therein as by threads 23.

The indicator 22 (Figs. 8-10) consists of a hollow cylindrical housing 24 provided with exterior threads 23 and having two inwardly projecting nubs 25 and 26. Holes 25a and 26a are bored diametrically thru nubr25 and into nulo 28 respectively as indicated. A spring 21 iits loosely inside of the hole 26a in nub 26 and in assembly is held under compression by a plunger 2,8 which extends from within the hole 26a in nub 2S thru hole 25a in nub `25 into a counterbored pointer 35.

portion 29 on the periphery of housing 24. That housing 24, thereby restraining the plunger from twisting. 1 1' A gear arm 33Y is pivotally supported atfone endfon a pin 32. The free end of gear arm 33 is provided with gear teeth 33a which mesh 'with a spur gear 34 which is rigidly assembled with a pointer 35 on a stud 36. A scalell is arranged beneath pointer 35. geararm 33 is provided a stud 31 which slides one. pad 38 on the base ol housing 24. Also on the under' side of the gear arm 33 is a stud 39 which is slotted and thereby holds a flat spring 40 which extends into a notch 4I in the plunger 28;; A helical spring42 having onej end secured to a post 42a in the base of housing 24 pulls the iiat spring 40 toward the left.v Sincejthe helical spring 21 thrusts the plunger 28 toward the right, positive contact between plunger 2S yand flat spring V40 is maintained aty all ties. 'A pin 43 mounted yin base of housing 24 acts as a stop to preventV thernovement of the gear arm 33 beyond the Yposition shown in Fig. 8 and a pin 44 acts as astopvto prevent "the movement of the pointer 35 and spur gear 34 assembly beyond the position shown in Fig. '8.

Atransparent cover`l is suitably secured to the top of housing Y24. Connecting section I2 of cylinder 9 and recess, 2 Itis a hole 45, axially parallel to the cylinder 9. In this connecting hole 45vis located a rod 1 with; one end abutting nut 2 and thus'ilush with the shoulder I4 between section I2 andersection II, and the other end extending into the counterbored recess 29 in housing 24- to contact plunger 28. The rod 1 is under compressive load betweenthe opposing thrusts of the spring 5 transmitted thru the nut 2 andthe spring A21 transmitted thru the plunger 28.

The anvil 46 is of course axially coincident with the cylinder 9. In servicerthe piece to be measuredisheld in position between the anvil 4B and the spindle 3.` The sleeve 4 is then turned, hence advancing spindle 3 by engagement of spindle threads'y 41f-and the nut 2 until contact is made on the piece ktobe measured, byboth spindle 3 andA anvil 46. Any additional movement of the sleeve 4` after actual contact with [the `piece to be measured, by the spindle v3 land the.Y anvil 46, results in withdrawal ofthe nut 2 from contact with the shoulder I4 and its movement along the thread 41 4of'thespindle3 compressing spring 5.

Secured to plunger 23 is a yoke 3B which slides on pads 3l on the base of This permits the compressed spring 21 to push out the plunger 28 of dial indicator 22 and it in turn pushes the rod 1 to maintain contact with the sliding nut 2. It will be noted that the spring 5 removes backlash between nut 2 and spindle 3 by its compressive stress and further holds pin 3 against thewall of slot I6 due to being assembled under torsional stress.` Y 1 vThe motion of the plunger 28 is transmitted thru the flat spring 40 to the gear arm 33 which in turn transmits it thru the spur gear 34 to the The pointer moves above scale 50 so that the extent of motion can be readily determined. The scale, preferably with a Zero reading in the center and graduations on each side, would serve to indicate in an arbitrary manner,

' the amount that the sliding nut 2 has been With- On the underside of the Y drawn'lrom the shoulder I4 which in turn would causea proportional compression of the spring 5.. Since in helical springs the deformation is a linear functionV o fv the Y stress, Vthe deilection -of pointer `35 isproportional'tothe stress exerted on the piece to be'measured between-anvil 46and spindle 3. Hence, successive measurements with theidentical stress or "feeF may be'mad'e by turning sleeve Iluntil pointer 35 reaches the same reading, VV`VThe precision with which this stress could be-duplicatedwould be governed only by theaccuracy and sensitivity of the dialY indicator which would be uniform at all times,-and not `by theab'ility of the operatorto-quantitatively reproduceY an exact ystress -each -time,- which involves the human variable. Y Y' s Y The micrometer` is set by placing a standard gage' block between'the anvil 46 and thespindle 3 and then turning the sleeve'4r-to'the corresponding setting.- At this point, the indicatorreading should be aero. Therlength of'- the-plunger 28 is adjusted by cap 28a. so that the pointer-comes to the zero'positionwhen the indicated measurement' correspondsto the A'thickness ofY the gage block used. After having been set in this manner, the" sensitivity` of the micrometer will be such thateven'an'inexperienced operator will be able to duplicate readings with great precision.r

Iclalnfit: y A 'In a micrometer having-a yoke shaped frame, ahollow cylindrical extension on the frame, a counterborein the end of said extension, a cylindrical' nut mounted.v in said counterbore for axial movement with respect thereto, a hollow plug engageable in the end of said counterbore thereby-limiting the axial movement of said nut within said counterbore, means for preventing rotational movement of said nut relative to the frame extension, a compression spring mounted between said nut and said plug andhavingits ends respectively secured to said nutand said plug, said spring being preloadedtoiproduce a combined axial and torsional bias between said nut and said plug, ,a barrelrotatably mounted on said frame extension, aspindle secured to said barrel and arranged to projectithru said hollow frame extension and threadablygengage said nut whereby rotation of said barrel advances said spindle relative to said nut, and indicating means on the frame responsiveto axial'movement of said nut member relative to the: frame. Y

DONALDgA. LUTTON. 

